A computer system is an arrangement which receives information, or data, from one or more data sources, processes the data through a routine to produce a result, and transmits the result to an output device, such as a display, a printer, or another machine that is in communication with the computer system. Computer systems are designed for both general purpose uses and for special purpose uses. They range in size from large ones to small ones, each depending upon its intended use. Small computer systems now include personal computers, such as laptop computers, notebook computers, handheld computers, and plastic card computers.
All of the aforementioned small computers include integrated circuit (IC) devices which are interconnected in some arrangement which processes the data under control of commands provided by a program. Energy, for operating each integrated circuit device, is supplied from an off-chip power supply. Some of the small computers are operated by energy supplied from a battery.
The rate of energy, or power, consumption for the small, battery operated, computer is an important system design criteria. Generally the computer system user desires the small computer system to operate from the battery for a duration that is as long as possible. Several computer system design techniques help to extend the duration of useful discharge of the battery energy, i.e., to extend the useful battery life between recharge cycles or replacement.
Since each typical small computer system includes several integrated circuit devices, it is very important to design each integrated circuit chip to consume as little energy, or power, as possible.
Integrated circuit devices, such as dynamic random access memory (DRAM) devices, are used in large numbers in each small computer system. Some dynamic random access memory devices include an on-chip high voltage source which generates a voltage V.sub.pp that is higher than the voltage V.sub.dd applied to the memory device from an off-chip voltage source, such as a battery.
The on-chip high voltage V.sub.pp is used for two purposes within the memory device. One purpose is for driving a selected wordline to the high voltage V.sub.pp so that, in spite of a threshold voltage drop lost because of the operation of an n-channel, enhancement-mode pass gate transistor, the selected storage cell still reaches the maximum restore voltage V.sub.dd. A second purpose is for applying the high voltage V.sub.pp to the gate electrode of the n-channel, enhancement-mode transfer gate transistor, which is interposed between a bitline and a sense node of a sense amplifier. In spite of the threshold voltage drop lost because of the transfer gate transistor, the sense node and the bitline both reach the voltage V.sub.dd when desired during operation.
An on-chip high voltage convertor is used to produce the voltage V.sub.pp which is higher than the off-chip supply voltage V.sub.dd. Such a high voltage convertor is fabricated right in the substrate and therefore uses some chip area. As the density of storage cells is increased in a memory chip, more and more chip surface is required for the high voltage supply circuits. A lower power and smaller chip area alternative is sought for efficiently boosting the voltage of the wordlines and the gate electrodes of the transfer gate transistors to a magnitude that is higher than the off-chip supply voltage V.sub.dd.